1. Technical Field
The present disclosure relates generally to measurement apparatuses and methods and, more particularly, to the quantitative mapping of thermomechanical properties using scanning probe microscopy.
2. Related Art
Knowledge of local thermomechanical properties of materials is invaluable for a broad spectrum of structural and functional materials including composites, coatings, pharmaceutical, and various drug applications that span a multibillion dollar market of polymer and organic materials. For example, in polymeric composites in which local phase transition temperatures vary between the constituent phases as well as at the interfaces of phases, local behavior of the polymeric composites may determine the overall thermal stability of polymeric coating, structural materials, and other structural and functional materials.
The methods for the analysis of the local thermomechanical behavior may be categorized into two groups. The first methodology utilizes uniform temperature fields when performing local mechanical testing. An example of such an approach is a variable temperature dynamic mechanical analysis (DMA). DMA enables temperature dependent measurements of mechanical properties to be taken of various materials. The analysis is performed within a chamber having controlled temperature and atmospheric conditions. However, this implementation results in a bulk of a sample material under test being heated thereby making it difficult to obtain accurate measurements of spatially resolved mechanical properties.
Alternatively, local heating methods enable a probe to locally confine a thermal field to a specified region of a sample and detect local mechanical properties. This local heating approach provides for improved spatial resolution of the measurements taken of the thermomechanical properties of the sample. Furthermore, by utilizing the local heating methodology, the thermal degradation of the bulk of the material is in large part avoided (e.g., the local heating method is substantially non-destructive).
Local thermal analysis (LTA) has emerged as a Scanning Probe Microscopy (SPM) based methodology that allows for melting and glass transition temperatures to be probed and measured at a 100 nanometer resolution. LTA has been employed in numerous applications in the fields of polymer science. Typical LTA may utilize various detection mechanisms to measure temperature dependent mechanical properties such as monitoring the displacement of a tip due to the penetration of a tip into a sample, the thermal expansion of the material under analysis, temperature dependent friction, and/or the change in thermal impedance. In some studies, active feedback is used in order for a heated probe to apply a constant pressure on a surface of a material. However, the detection mechanisms described above may be insensitive to changes in the dissipative properties that characterize the material sample (e.g., changes in the loss modulus) and therefore preclude a high-accuracy determination of the transition temperature of the material. A contact area between the probe and the material may vary due to changes in the effective material properties preventing an accurate quantitative interpretation of LTA mechanical and thermal dissipation data.